Adaptive behavioral reactions of reaching in rats following discrete somatosensorimotor cortex lesions

To test the effects of lesions of forelimb somatosensorimotor subareas on the reaching behavior, the rats were trained to reach for food pellets in a horizontal tube and through a grid. Reaching attempts were monitored by continual movement recording using magnetic induction and reaching success was quantitatively evaluated. In rats with bilateral lesions centered over the forelimb motor subarea (FMCL), reaches with the preferred forepaw were accompanied by reaching attempts with the nonpreferred forelimb. The latter declined over the recording period but larger residual movements were still observed at the end. Relative to control group, the performance of rats with FMCL was significantly decreased in both reaching tasks, however the reaching success into tube was significantly lower than through a grid. Rats with lesions centered over forelimb cutaneous representation (FCRL) showed signs of tactile deficit. Chosen reaching tactic represented an attempt to compensate for the tactile deficit. No reaches with the nonpreferred forepaw were observed. Relative to controls, the reaching success in rats with FCRL was decreased by the same amount in both reaching tasks. When reaching into the tube, the rats with FCRL performed significantly better than rats with FMCL over the whole recording period; when reaching through the grid no statistical difference in performance was observed between groups though the rats with FMCL performed better than the rats with FCRL. The discrete somatosensorimotor cortex lesions did not only result in different direct reaching deficits and performance, but also resulted in different behavioral reactions.